Ethylene Glycol (EG) is a commodity used as antifreeze, in deicing products for aircraft and for the production of detergents, paints, cosmetics and polymers (such as polyesters). The process leading to the production of Ethylene Glycol from Dimethyl Oxalate (DMO) has been in development for more than a decade. Some of the advantages of synthesizing EG from DMO or Diethyl Oxalate (DEO) include: (a) the ability of using syngas generated by massive reserves of coal, thus reducing the demand for oil (which is the main raw material that produces an ethylene oxide intermediate), (b) a more profitable use of coal chemicals as compared to simple production of electricity for inferior and high moisture coal, (c) the capacity of stabilizing the price for EG as a commodity linked to the dimension of coal deposits, and (d) the capability of controlling CO2 emitted through separation inside gasification installations, followed by other possible uses or storage/sequestration.
Furthermore, extensive reserves of low sulfur subbituminous coal exist in Wyoming, and these reserves are currently used for combustion in power plants despite having a water content that decreases the coal's heating value. The coal's water content has shifted interest toward using this valuable resource more efficiently and profitably. Gasification is one of the main techniques used as a more efficient use of coal. In particular, with gasification, water becomes a component of the reaction and the syngas produced can be used to produce higher value substances such as Dimethyl Oxalate and/or Diethyl Oxalate.
The use of a DMO/DEO hydrogenation reaction may include a Cu/SiO2 catalyst, which may include one or more metallic additives. Cu/SiO2 catalyst shows selectivity toward Ethylene Glycol (EG) and the stable Methyl Glycolate (MG) intermediate. Mesoporous materials (e.g., M41S group), hexagonal mesoporous silica (HMS), SBA-n, FSM-16, MCF, and MCM-41 have been reported as a silica (SiO2) support. Furthermore, for increased internal mass transfer and stability and development for industrial implementation of the monolithic supports, Cu/SiO2/cordierite may be used. However, the supports contain strong acid sites that will induce the intermolecular dehydration of ethylene glycol to ethanol, while the strong basic sites catalyze the formation of 1,2-butanediol.
Other supported metallic catalysts may include Ag/MCM-41 (Ag/SiO2), Au—Ag/SBA-15. However, industrial applicability may be limited for these catalysts due to the price of certain metals.
The reaction of DMO (or DEO) to EG may occur in two steps, having a methyl glycolate (MG) intermediate:CH3OOCCOOCH3+2H2→CH3OOCCH2OH+CH3OH ΔHo=−30.03 kJ/mol  (R1)CH3OOCCH2OH+2H2→HOCH2CH2OH+CH3OH ΔHo=−28.70 kJ/mol  (R2)
As mentioned above, the resultant EG can be further hydrogenated/dehydrated to ethanol, and other products might be generated like 1, 2-butanediol, ethane etc.HO—CH2—CH2—OH+H2→CH3—CH2—OH+H2O ΔHo=−87.20 kJ/mol  (R3)
The hydrogenation reaction of DMO or DEO with a Cu/SiO2 catalyst is generally operated at ˜200° C., ˜2 Mpa. It is considered that Cu as a catalyst allows the somewhat selective hydrogenation of C—O bonds without breaking C—C bonds. However, synthesis of Cu/SiO2 catalysts by processes known in the art suffer from setbacks including:
poor stability of the metal-oxide interface and relatively fast sintering of copper aggregates, as well as over-reduction of surface cuprous species into Cu0 during pretreatment and reaction;
relatively low catalytic activity and deactivation when operated at a high liquid hourly space velocity (LHSV) due to weak mechanical properties;
in order for porous catalyst sites to be accessible, DMO/DEO has to be able to enter through the pores of the catalyst, and pore size and particle size are difficult to predict and control;
most of the syntheses for this class of catalysts are slow and susceptible to generating materials of uneven activity. For example, current syntheses result in catalysts that either have selectivity for EG or efficient conversion of DMO/DEO, but not both selectivity and efficient conversion.
One method of Cu/SiO2 catalyst formation is deposition-precipitation of copper using ammonia evaporation (AE) or urea decomposition (UD) on silica sol, sol-gel (SG) using Tetraethyl Orthosilicate (TEOS) or various pre-prepared siliceous based supports (MCM-41 SBA-15, ZSM5). Ammonia evaporation (AE) consists of adding ammonia to pH>10 for the formation of tetraamino cupric complexes followed by heating which eliminates ammonia by boiling (ammonia evaporation), which adjusts the pH to around 7 or less to promote precipitation of Cu compounds. In addition to the variation in copper deposition as a function of the rate of pH change and temperature during boiling associated with slow copper compound deposition, the ammonia evaporation method may be hazardous with risk of explosions, intoxications, and environmental damage upon scale up.
There is a need in the art for controlled methods of synthesizing hydrogenation catalysts that promote faster catalyst deposition and are safer and more environmentally favorable. There is also a need in the art for hydrogenation apparatus and catalysts, and methods of making such catalysts, that have high product selectivity and starting material conversion.